5MG Tofacitinib inhibits Janus kinase. It functions by preventing the Janus kinase enzyme from doing its job. As a result, rheumatoid arthritis joint damage and inflammation are reduced. It is a disease-modifying anti-rheumatic medication (DMARD), which inhibits the immune system to work. There are three different ways to get tofacitinib: as a tablet (Xeljanz), an extended-release tablet (Xeljanz XR), and as an oral solution.